1. Field of the Invention
The present invention relates to an electrophotographic photoconductor, and an image forming apparatus and a process cartridge using the electrophotographic photoconductor.
2. Description of the Related Art
In recent years, in terms of saving space in offices, expanding business opportunities, and the like, higher speed, smaller size, colorization, particularly higher image quality, easy maintenance, and the like have been desired for image forming apparatuses. These are associated with improvements in the electrical properties and durability of electrophotographic photoconductors, and regarded as problems to be solved.
In terms of improving easy maintenance, a reduction in the frequency of replacement of electrophotographic photoconductors is mentioned. This is decreasing image defects derived from the electrophotographic photoconductors as much as possible over a long period, and is none other than achieving longer life of the electrophotographic photoconductors. In addition, this is also associated with achieving higher image quality of output images over a long period. In order to solve the above problems in the electrophotographic photoconductors, attempts have been made to reduce image defects derived from electrophotographic photoconductors during a long period of use, and a large number of developments for longer life of electrophotographic photoconductors have been reported. In order to achieve longer life of electrophotographic photoconductors, it is necessary to improve durability against various hazards to the electrophotographic photoconductors during image formation. Here, the hazards are broadly divided into two types, mechanical hazards and chemical hazards.
As one example of the mechanical hazards, a hazard derived from cleaning means (the so-called blade cleaning) for removing a toner remaining on an electrophotographic photoconductor is known. The blade cleaning is means that forcedly removes a toner from an electrophotographic photoconductor by abutting an elastic member, such as a cleaning blade, on the photoconductor, and is space-saving and has large toner removal ability. Therefore, the blade cleaning is known as means effective in achieving smaller size of image forming apparatuses. But, a problem of such a cleaning system is that the elastic member, such as a cleaning blade, is directly abutted and slid on the electrophotographic photoconductor, and therefore, the mechanical stress on the electrophotographic photoconductor is very large, and the outermost surface of the electrophotographic photoconductor is likely to be abraded. Therefore, techniques for inhibiting the abrasion of an electrophotographic photoconductor by laminating a high hardness protective layer are proposed (for example, see Japanese Patent Application Laid-Open (JP-A) No. 05-181299, Japanese Patent Application Laid-Open (JP-A) No. 2002-06526, Japanese Patent Application Laid-Open (JP-A) No. 2002-82465, Japanese Patent Application Laid-Open (JP-A) No. 2000-284514, and Japanese Patent Application Laid-Open (JP-A) No. 2001-194813).
One example of the chemical hazards includes an electrostatic hazard caused by the application of electrostatic stress to an electrophotographic photoconductor. In the usual image forming process, a charge is applied to an electrophotographic photoconductor surface, and the electrophotographic photoconductor surface is charged to a predetermined potential, and then, the charge applied to the surface is removed via the photoconductor by the exposure of the electrophotographic photoconductor. At this time, the charge passes through the layers (for example, a surface layer, a charge generation layer, a charge transport layer, and an intermediate layer) of the electrophotographic photoconductor, and thus, electrostatic stress is applied to the electrophotographic photoconductor. Currently, most of widespread electrophotographic photoconductors contain organic materials. Therefore, in the current electrophotographic process such that charging and discharging are repeated, the organic materials constituting the electrophotographic photoconductor are gradually deteriorated by the electrostatic hazard, causing a decrease in electrophotographic properties as mentioned as the occurrence of charge trapping in the layers, and a change in charging properties, light attenuation properties, and the like.
In addition, as one example of the chemical hazards, a hazard due to acidic gases, alkaline gases, and the like produced when the surface of an electrophotographic photoconductor is charged to apply a charge, or the like is also known. Acidic gases, such as ozone and nitrogen oxides, are generated in the vicinity of a charging device (for example, see KONICA Technology Report Vol. 13 (2000)). Therefore, when an electrophotographic photoconductor is exposed to these acidic gases, the charge-transporting materials, such as the hole-transporting material and the electron-transporting material, contained in the electrophotographic photoconductor are deteriorated by the acidic gases (for example, see Journal of Imaging Science 32: 205-210 (1988)), and the properties of the electrophotographic photoconductor decrease. When an electrophotographic photoconductor having short life is used, deterioration due to acidic gases often occurs only in the outermost layer of the electrophotographic photoconductor, and the amount of the deteriorated components is also small. On the other hand, when an electrophotographic photoconductor having long life is used, deterioration due to acidic gases may reach the inside of the electrophotographic photoconductor, and many deteriorated components are contained in the electrophotographic photoconductor. As a result, a decrease in image density, scumming, the deterioration of the uniformity of images during continuous output, and the like occur, and a problem is that the output of images having high image quality cannot be maintained during a long period of use.
In order to solve the problems of the chemical hazards, techniques of adding an antioxidant to a charge transport layer and a surface layer to inhibit the deterioration of the charge-transporting material due to acidic gases are proposed (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2006-099028 and Japanese Patent Application Laid-Open (JP-A) No. 2010-139618). In addition, techniques for reducing the gas permeability of a charge transport layer and a surface layer in order to inhibit acidic gases from permeating into these layers are proposed (for example, see Japanese Patent Application Laid-Open (JP-A) No. 03-45962 and Japanese Patent Application Laid-Open (JP-A) No. 07-281463). In addition, techniques for inhibiting the generation of discharge products (acidic gases) in a charging step are proposed (for example, see Japanese Patent Application Laid-Open (JP-A) No. 09-026685 and Japanese Patent Application Laid-Open (JP-A) No. 2002-229241).
But, even if these proposed techniques are used, an essential improvement is not achieved because relatively large amounts of oxidatively deteriorated components are contained in the electrophotographic photoconductor, and a problem is that the output of high quality images cannot be maintained when the electrophotographic photoconductor is used for a long period.
In addition, in recent years, techniques of modifying electroconductive fine particles or insulating fine particles with a compound having the function of an antioxidant, and adding the electroconductive fine particles or the insulating fine particles to a surface layer have been known (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2011-043574 and Japanese Patent Application Laid-Open (JP-A) No. 2012-173511). When insulating fine particles are modified with a compound having the function of an antioxidant, it is essential to add a charge transport agent to a surface layer in order to reduce the potential after exposure. Therefore, the mechanical durability and the chemical durability are poor. In addition, also when electroconductive fine particles are modified with a compound having an antioxidant function, a sufficient function cannot be exhibited in some cases depending on the modifying compound species.
Therefore, under the present circumstances, there is a strong need for the development of an electrophotographic photoconductor in which oxidative deterioration and abrasion due to a long period of use are extremely reduced, defects associated with the output image quality of an image forming apparatus are reduced, and excellent image quality is maintained over a long period, and an image forming apparatus and a process cartridge using the electrophotographic photoconductor.